Diels-Alder reactions in pyridinium based ionic liquids

Diels-Alder reactions have been investigated in pyridinium based ionic liquids. These solvents are found to be more effective compared to the organic solvent studied, in enhancing the reaction rate and product yields. Recycled ionic liquids also gave excellent results.     

Using geminal dicationic ionic liquids as solvents for high-temperature organic reactions

[reaction: see text] Several organic reactions conducted at high temperatures, including the isomerization reaction, the Claisen rearrangement, and the Diels-Alder reaction, were investigated in three geminal dicationic ionic liquids with high thermal stability. High to moderate yields of the products for most entries were obtained. Advantages of these approaches are discussed. These ionic liquids were shown to be recyclable. The utility of these ionic liquid solvents for high-temperature organic reactions was demonstrated.     

Converting exo-selective Diels-Alder reaction to endo-selective in chloroloaluminate ionic liquids

The endo:exo ratio of 0.35:1 for the reaction of cyclopentadiene with methyl methacrylate observed in organic solvents can be converted to 3:1 in chloroaluminate ionic liquids with their effective reuse in Diels-Alder reactions.     

The cosolvent-directed Diels-Alder reaction in ionic liquids

The rate constants of a bimolecular Diels-Alder reaction in binary mixtures of ionic liquids prepared in molecular solvents were analyzed to investigate the effect of viscosity of the medium and solvent effect. In this connection, we have carried out the Diels-Alder reaction of anthracene 9-carbinol with N-ethyl maleimide in binary mixtures of pyridinium-based ionic liquids, 1-butyl-pyridinium tetrafluoroborate, 1-butyl-3-pyridinium tetrafluoroborate, and 1-butyl-4-methyl pyridinium tetrafluoroborate in water, methanol, and chloroform at 298.15 K. The rates of reaction decreased, caused by gradually increasing the volume fraction of ionic liquids in solvents for all three ionic liquids. The kinetic results demonstrate a successful application of the pairwise interaction model built upon the concept of enforced hydrophobic hydration. A temperature-dependent study of kinetics of the Diels-Alder reaction was carried out in the binary mixtures of ionic liquids in water and was explained by the entropy-enthalpy compensation effect based upon activation parameters. Kinetics of the Diels-Alder reaction in highly aqueous medium was noted to be entropically driven.     

High viscosity of ionic liquids causes rate retardation of Diels-Alder reactions

Second order rate constants, k2 have been determined for three bi-molecular Diels-Alder reactions to demonstrate that the high viscosity of ionic liquids can be a detrimental property in carrying out Diels-Alder reactions, if ionic liquids are employed as solvent media. It is possible to enhance the reaction rates of the reaction if a co-solvent is mixed in pure ionic liquid used as a solvent.     

Fluorous imidazolium room-temperature ionic liquids based on HFPO trimer

Imidazole substituted with a polyfluoropolyether chain based on HFPO trimer combined with various polyfluoroalkyl triflates produced novel highly fluorous ionic liquids. Their metathesis with four different anions generated a final set of 20 fluorous ionic liquids of waxy or viscous liquid character, which are all soluble in perfluorinated solvents. Two model reactions using selected ionic liquid, the opening of a THF ring with benzoyl chloride under Friedel-Crafts conditions and substitution of benzyl chloride with sodium azide, led to decomposition of the ionic liquid. However, Diels-Alder reaction of 2,3-dimethylbuta-1,3-diene with dimethyl acetylenedicarboxylate in a fluorous ionic liquid resulted in a reasonable enhancing of the reaction rate with smooth recycle of the fluorous solvent. The fluorophilicity of these fluorous ionic liquids ranges from more than 10 for water, toluene or dichloromethane to less than 0.2 for acetonitrile or methanol.     

Dy(OTf)3 Catalyzed Reaction of Indole with Aldehydes and Ketones in Ionic Liquids

The use of environmentally benign reaction media is very important in view of today' s environmentally con scious attitude. In connect with this, room temperature ionic liquids that are air and moisture stable have received a good deal of attention in recent years as novel solvent systems for organic synthesis. A number of reactions such as Friedel-Crafts reactions, Diels-Alder cycloadditions, hydrogenations, and Heck reactions have employed ionic liquids as solvents. Among them, the Friedel-Crafts reaction[1] is of great synthetic significance in view of laboratory synthesis and industrial production. Recent studies showed that Friedel-Crafts reaction of indole with carbonyl compounds proceeded readily in aqueous media. [2] However, the aqueous reactions suffer from some common problems,such as tedious work-up, reuse of catalyst and so on.     

Michael addition kinetics of ethyl acetoacetate and 2-ethylhexyl acrylate in ionic liquids

The Michael addition is one of the most common and versatile methods for making carbon–carbon bonds, however little is known about the potential of utilizing ionic liquids as solvents in these reactions. Initial work from our laboratory is presented, showing that model imidazolium- and phosphonium-based ionic liquid solvents can be used as effective reaction media in the Michael addition. Kinetic data are also reported and the results indicate that the use of ionic liquids as reaction media resulted in an observed rate enhancement when compared with more common organic solvents such as toluene, THF, and DMF. Observed rates were comparable to those observed in DMSO.     

Selective chemical reactions in supercritical carbon dioxide,water, and ionic liquids

Abstract

Alternative solvents such as supercritical carbon dioxide, water, and ionic liquids are receiving an increase of interest as better replacements for conventional solvents in chemical reactions. They have been called sustainable green solvents because they are highly promising reaction mediums for organic synthesis. This review presents an overview of some selected chemical reactions that have been developed in these green solvents with a particular emphasis on metal-catalyzed reactions.     

离子液体在有机反应中的应用

室温离子液体，由含氮的有机阳离子和无机阴离子组成，可溶解各种有机、无 机、金属有机化合物。它们没有蒸气压、不易燃、容易循环使用。近年已发现，离 子液体可广泛地用于许多过渡金属化合物和酶催化的反应。着重讨论这方面的发展 状况。     

Silicon carbide passive heating elements in microwave-assisted organic synthesis

Microwave-assisted organic synthesis in nonpolar solvents is investigated utilizing cylinders of sintered silicon carbide (SiC)--a chemically inert and strongly microwave absorbing material--as passive heating elements (PHEs). These heating inserts absorb microwave energy and subsequently transfer the generated thermal energy via conduction phenomena to the reaction mixture. The use of passive heating elements allows otherwise microwave transparent or poorly absorbing solvents such as hexane, carbon tetrachloride, tetrahydrofuran, dioxane, or toluene to be effectively heated to temperatures far above their boiling points (200-250 degrees C) under sealed vessel microwave conditions. This opens up the possibility to perform microwave synthesis in unpolar solvent environments as demonstrated successfully for several organic transformations, such as Claisen rearrangements, Diels-Alder reactions, Michael additions, N-alkylations, and Dimroth rearrangements. This noninvasive technique is a particularly valuable tool in cases where other options to increase the microwave absorbance of the reaction medium, such as the addition of ionic liquids as heating aids, are not feasible due to an incompatibility of the ionic liquid with a particular substrate. The SiC heating elements are thermally and chemically resistant to 1500 degrees C and compatible with any solvent or reagent.     

离子液体的制备及其在酶催化反应中的应用

离子液体,尤其是非水溶性离子液体可以作为一种溶剂或酶的载体用于非水相酶促反应中,也可以用于双相体系中的酶促反应。本文概括性介绍了常见离子液体的制备,总结和讨论了离子液体中酶的活性、稳定性、反应选择性以及各类酶在离子液体中的催化反应行为。离子液体的物性及其与酶的相容性对酶本身及酶促反应都有很大的影响。在非水相酶促反应中,离子液体的极性作用不遵从通常用来判别大多数有机物溶剂行为的规则,比如lgP规则。     

Sonochemistry and sonoluminescence in ionic liquids, molten salts, and concentrated electrolyte solutions

Ionic liquids have favorable intrinsic properties that make them of interest as solvents for various chemical reactions. The same properties that make the liquids effective solvents also make them interesting liquids for studies involving sonochemistry, acoustic cavitation, and sonoluminescence. Recent interest in using ultrasound to accelerate chemical reactions conducted in ionic liquids necessitates an understanding of the effects of acoustic cavitation on these solvents. Here, we review our previous results on the effects of cavitation on some room-temperature ionic liquids, including the sonoluminescence spectra of molten salt eutectics and concentrated aqueous electrolyte solutions. In all cases, regardless of the essentially nonexistent vapor pressure of the solution atomic and small molecule emitters are observed in the spectra which arise from sonolysis of the ionic liquids.     

Efficient synthesis of β-chlorovinylketones from acetylene in chloroaluminate ionic liquids

A method for the Friedel-Crafts-type insertion reaction of acetylene with acid chlorides in chloroaluminate ionic liquids is presented. The use of ionic liquids not only serves to avoid the use of carbon tetrachloride or 1,2-dichloroethane but also suppresses side reactions, notably the polymerization of acetylene, which occurs in these chlorinated solvents. Consequently, the products can be isolated using a simpler purification procedure, giving a range of aromatic and aliphatic β-chlorovinyl ketones in high yield and purity.     

Ionic liquid-catalyzed Diels-Alder reaction of levopimaric acid with quinones

Diels-Alder reactions of levopimaric acid with quinones are strongly accelerated in the presence of ionic liquids (imidazolium salts) as catalyst.     

Ionic liquids in enzymatic catalysis and biochemical methods of analysis: Capabilities and prospects

The first Russian review systematizes and discusses the most important and promising published data on the use of ionic liquids in biocatalysis and, especially, biochemical methods of analysis. Studies on the use of ionic liquids as solvents for enzymes, new reaction media for enzymatic reactions, and components of the biosensitive layers of sensors are analyzed. The physical and chemical properties of ionic liquids used in biocatalysis are discussed. The advantages of ionic liquids over the usual solvents in homogeneous and heterogeneous reactions with the participation of enzymes from various classes are demonstrated, procedures for the coimmobilization of biocatalysts and ionic liquids with cellulose onto polymer supports and electrodes are described, and prospects for the use of enzyme-ionic liquid compositions in biochemical methods of analysis are considered.     

Matrix-assisted laser desorption/ionization mass spectrometry for the characterization of ionic liquids and the analysis of amino acids, peptides and proteins in ionic liquids

Ionic liquids are interesting solvents for a number of applications in chemistry and biotechnology. We characterized five different ionic liquids by laser desorption/ionization (LDI) and by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) and studied the analysis of amino acids, peptides and proteins dissolved in these solvents. Signals of both anions and cations of the ionic liquids could be observed both in LDI- and in MALDI-MS. In the latter case, adduct formation between anions and cations of the analytes was observed. Amino acids, peptides and proteins could be analyzed in ionic liquids after addition of matrix substances. Sodium and potassium adducts were not observed in any analysis involving ionic liquids. Low molecular mass compounds and peptides could be analyzed best in the presence of water-immiscible ionic liquids, whereas proteins gave the best results in water-miscible ionic liquids. Optimal analysis conditions such as molar matrix-to-analyte and ionic liquid-to-matrix ratios were determined. Homogeneity of samples in the presence of ionic liquids was reduced compared with classical MALDI preparations. Relative quantitation of amino acids was possible using isotope-labeled internal standards. MALDI-MS thus can be used for the analysis of chemical reactions and the screening of enzyme-catalyzed reactions in ionic liquids and for the analysis of the biocatalysts dissolved in these solvents. Theoretical aspects of ion formation in the presence of ionic liquids both in LDI and MALDI analysis are discussed.     

A rationalization of the solvent effect on the Diels-Alder reaction in ionic liquids using multiparameter linear solvation energy relationships

The Diels-Alder reaction between cyclopentadiene and three dienophiles (acrolein, methyl acrylate and acrylonitrile) having different hydrogen bond acceptor abilities has been carried out in several ionic liquids and molecular solvents in order to obtain information about the factors affecting reactivity and selectivity. The solvent effects on these reactions are examined using multiparameter linear solvation energy relationships. The collected data provide evidence that the solvent effects are a function of both the solvent and the solute. For a solvent effect to be seen, the solute must have a complimentary character; selectivities and rates are determined by the solvent hydrogen bond donation ability (alpha) in the reactions of acrolein and methyl acrylate, but not of acrylonitrile.     

Improved preparation and use of room-temperature ionic liquids in lipase-catalyzed enantio- and regioselective acylations.

Polar organic solvents such as methanol or N-methylformamide inactivate lipases. Although ionic liquids such as 3-alkyl-1-methylimidazolium tetrafluoroborates have polarities similar to these polar organic solvents, they do not inactivate lipases. To get reliable lipase-catalyzed reactions in ionic liquids, we modified their preparation by adding a wash with aqueous sodium carbonate. Lipase-catalyzed reactions that previously did not occur in untreated ionic liquids now occur at rates comparable to those in nonpolar organic solvents such as toluene. Acetylation of 1-phenylethanol catalyzed by lipase from Pseudomonas cepacia (PCL) was as fast and as enantioselective in ionic liquids as in toluene. Ionic liquids permit reactions in a more polar solvent than previously possible. Acetylation of glucose catalyzed by lipase B from Candida antarctica (CAL-B) was more regioselective in ionic liquids because glucose is up to one hundred times more soluble in ionic liquids. Acetylation of insoluble glucose in organic solvents yielded the more soluble 6-O-acetyl glucose, which underwent further acetylation to give 3,6-O-diacetyl glucose (2-3:1 mixture). However, acetylation of glucose in ionic liquids yielded only 6-O-acetyl glucose (>13:1 and up to >50:1).